Facebook added new measurement tools on Tuesday that allow companies to track people who are entering their stores and deliver ads directly targeted to people in the surrounding area.

Facebook is building the most sophisticated, surveillance-fueled advertising business in the world. But, as Facebook points out on its blog, 90% of retail shopping still happens in physical stores, so it's looking for ways to combine the real-life experience of shopping with the fact that 45% of people have their phone out while shopping to help them browse.

In order to build this advertising business, Facebook will have to track the stores all of its users enter.

Last summer, Facebook handed out "beacons" to some retailers — little devices that sensed when smartphones were nearby and could push ads to those phones.

The social network's new ad-targeting system only works for those who have location services turned on. Many services either require location services or surreptitiously ask you to turn them on when you first open the app.

You could always turn your location services off, but then you'd miss out on the ubiquitous surveillance — er, sweet deals.